Malvolio enters, scolding the revellers and telling Sir Toby that Olivia told him to inform Toby that if he won’t behave, she will be quite happy to see him out of her house, even though he is her relative. Toby and his pals treat him scornfully, Toby calling Maria to bring him more wine. “You won’t do such thing”, says Malvolio and exits. In their conversation after he leaves, Maria calls him explicitly a Puritan – there were some hints identifying him earlier as such, for instance when Toby says “Dost thou think because thou art virtuous there shall be no more cakes and ale?” Cakes and ale were sold during church fetes and as such hated by Puritans. Now Maria plans to play a trick on him, using his particular weakness, since she knows Malvolio is quite full of himself. She is going to write letters, mimicking Olivia’s hand, expressing Olivia’s alleged admiration of him. She is also going to tell Toby and Andrew where she has planted them, so that they can observe Malvolio reading them. The others applaud her plan and go to bed, but not before Andrew laments that he is going to be quite poor if he doesn’t marry Olivia and Toby cheering him up with a promise of some mulled wine.
I think Shakespeare is playing very subtly with his audience’s expectations. He assumes his audience, like he, do not like Puritans (and there was no fear of having any in the audience, because Puritans hated the theatre) and so he casts Malvolio as one. But in this particular situation, Malvolio acts only as a messenger from Olivia, who is justifiably tired with having her party-loving uncle/cousin (it’s kind of vague) constantly around. But the anger of Toby and his friends is concentrated on Malvolio, not on Olivia. Malvolio may be a dour Puritan and a killjoy (or “aguafiestas”, a delightful Spanish word I learnt today), but he is also in the right. We all know there is nothing as annoying as a party next door when we need to sleep – or as annoying as police officers sent by these grouchy neighbours when we are having such a good time!